Method of purifying beryllium oxide



Patented Nov. 21, 1950 unimo stair-ss ev-.arp-

fr ortica America .as .represented by the AUnited vStates Atomic "Energy Commission ApplicationlNovember 19, 1948, Serial' No..61;ll38

aclantis. (c1. 23-14'00 y This invention relates to a process for the preparation of `compositions and structures of beryllium oxide, and, more particularly, to a process `for :the preparation of beryllia of improved purity and decreased density.

An object of this invention is to provide a process for the transfer and purification of beryllium oxide.

which :make fit .particularly 'suitable for use at high :temperatures ras either an insulating A-Inaterial-or a refractory.-

A kson further object lof .this invention is to, .provide a 'process `for'the rapid volatilizationoi beryllium Ioxide thereby Y.affording a simple, -.rapid and expedient means for batch or continuous operations involving Vthe 'transfer of beryllium oxide. v

Other objects and advantages fof this invention will bezapparent upon further examination of the specification.

We have discovered that beryllia heated in contact with steam reacts readily at elevated temperatures. Apparentlyfthis reaction of steam with beryllia involves the formation of a volatile beryllium compound such as beryllium hydroxide or hydrates of beryllium hydroxide in vapor form. W hen this volatile reactionproduct comes in contact with a coolersu-rface orv/hen the-entire beryllia-steam syst-em 'itself is cooled -`in -any suitable manner, -the high temperature reaction is vreversed resulting in the `4deposition k.of kneedle-- like beryllia crystals :measuring approximately 0.2 millimeter in length. These small hexagonal crystals have an extremely 'high luster, 4are quite soit-and show no evidence Aof'tarnishi-ng.

In accordance with "the :principal -zembodiment of this invention, steam is passedover beryllia at an elevated temperature. The rate'ofreaction between beryllium oxide and stiam increases eX- ponentially withthelternperatnre. :The nrocess cento rate 'for 'the above-described iberyllia-steam reaction tincreases with the increase vin the flow rate of steam. At a Agiven temperature anda constant steam pressure "an increase lin `the rate of mass now of steam results in -an increase `in the reaction rate. However this increasein 're- .action rate isnot proportionalto the increase in the lsteam now rate, but tends 'to increase `less rapidly toward a'limiting value. In'carryingout process of this invention it is preferred that :steam pass over Vthe beryllia at a mass -flow'rate of .atleast 0.1 mol of steam per minute.

In thepractice of Uthe process of this 'invention. `the starting Amaterial may be in the Iform of either beryllia powder or lpellets lof beryllia. On comparison of the 'reaction rate obtained when using unpressedberyllia-powder with values obtained byreacting berylia pellets with steam, only a Slight difference in the 4rate'oi" reaction has been observed where the pellet surface area has been varied up to a factor of "fh/e. Forexample at a temperature/10i "11500" C. and a steam nowrate of 0.11 mol/min. at atmospheric pressure, the beryllia removed yby the `steam vfrom the starting material lis lonly a minor function of the 'surface area of `the pellet. Under -such conditions, the rate-area coefficient is 1.-'7 x10-4 Vgram per cm.2 per minute.

In the'following examples the beryllia pellets were made from vabout 5 grams Vof Vhigh-fired beryllia `powder of about 125 mesh size mixed with, 40.5 cubic centimeter of 6 molarnitric acid as a binder. The Wet pellets were .then Asuitably formed 'by means of a die and arbor press and then dried for abouteighteen hours:at`100 C. followed by 'firing for one hour'in stagnant air at 1650 C. L

Referring to Figures l and an apparatus suitable for carrying out the A,process of this invention and usedinthefollowing examples consisted of a ptatinurn Macross-section tray l to hold the starting material Whichewas inserted into the center portion of a fmullite tube 3.6 centimeters inside kdiameter and 75 centimeters long. The trbe 2 was heated by a furnace 3 which surrounds the :central kportion.

To generate steam, `the apparatus fincluded ra round-bottomed flask 1i -made of llow falkali content borosilicate glass (enclosed in 'a `suitable heating 4mantle ii), -a "baffle '6 to prevent Jmechanical transport o'f Water, 'a preheater '-'l :of glass tubing wound with resistance Wire, fand a thermocouple 13 to indicate fthe prheater `temperature. The preheater l -was fseal-ed Vto Ione end 'Oi the mlillte tubing 2 i at 9 with Ifa glasslike sealing material. The preheater 1, seal 9, and exposed mullite tubes 2 were lagged with asbestos paper l and magnesia Il insulation. The mullite tube 2 at the other end was sealed with glasslike material to a heat resistant borosilicate glass joint l2 into which was fitted an assembly incorporating an optical window I3 and an exit tube Il! connected to a water-cooled condenser (not shown). The sample may be introduced at this joint l2. The temperature of the mullite 2 was measured by a thermocouple i5 of platinum and a platinum-rhodium alloy and the pellet temperature was determined by an optical pyrometer I6.

For steam pressures below atmospheric, a high vacuum pump (not shown) was attached to the apparatus at l1 through a stopcock I8, the watercooled condenser was replaced by a carbon dioXide-acetone-cooled trap (not shown) and a stopcock I9 was added between the water flask t 4 and the furnace 3. A monometer 20 was attached to the apparatus near the exit end of the mullite tube. For experiments at very low distillation rates the water flask 4 was replaced by a double walled flask (not shown) with amyl acetate refluxed in the space between the walls.

As a convenient means for the collection of the steam-treated BeO, a metal tube which served as a cold finger 2! was inserted into the reaction tube 2, the tip of this cold finger being made of thin-walled 1/8" outside diameter platinum tubing which was sealed to Tae outside diameter copper tubing with gold wire as solder. The copper tubing was then sealed with silver solder to larger copper tubing, which, in turn was sealed to the glass tubing sealed through the reaction tube to the outside. The tip of the platinume tube was about 1 centimeter removed from the beryllia pellet on the side opposite the steam source. Nitrogen gas was used as a coolant in this cold finger.

EXAMPLE I Weight Per Time Cent BeO Hours Transferred X-ray examination of the product showed that the white cotton-like crystal mass which condensed on the cold finger within the tube was pure beryllia.

A further embodiment of this invention com- 'prises the removal of certain impurities normally associated with commercial beryllium oxide by Y Y heating commercial beryllium oxide in contact with steam at temperatures within the saine temrperature range set forth for use in the lrst embodiment of this invention. Both metal and non-metal impurities, for example, impurities containing silver, aluminum, iron and silicon in the form of the metal oxides or salts, and which are normally associated with beryllium oxide'can be removed therefrom by this process as shown in Example II.

EXAMPLE II Approximate Concentration of impurity, Per Cent Element Original BeO Pellets BeO Crystals not detected. ca. 0.01. not detected. ce. 0.01.

EXAMPLE III Experiments similar to those described in Example I were carried out at a steam pressure of 1 atmosphere with steam passing over the samples at a rate of 0.11 mol/min. in a tube measuring 3.6 centimeters inside diameter. The percentages of beryllia volatilized by the steam at various temperatures are shown as follows:

Weight Per Temperature, Cent BeO C. Transferred in 2.5 Hours EXAMPLE IV The following tabular data illustrate the degree to which the rate for the beryllia-steam reaction is affected by the ow rate for steam.

Effect of steam flow rate on the BeC-steam reaction Amount of Steam Weight Per Hdglsm Flow l Rate, Tlp" Cent BeO ml'Jmin. liter/min. Transferred 0. 1 0. 81 1, 500 0. 93 0. 1 0.81 l, 500 0. 90 0. 25 2. 02 l, 500 1. 00 0. 5 4. 05 l, 500 l. 2l 0. 5 4, 05 1,500 l. 17 1.0 8. l0 1. 50D 1.45 2. 0 16. 20 1,500 1. 58 6.0 48. 60 1, 500 2. 10

1 Volume flow rate at furnace temperature.

The process and apparatus disclosed in the present application are intended to be illustrative rather than limiting in scope. The numerous modications and equivalents thereof will be apparent to those skilled in the art and are therefore included in the scope of the present invention. Therefore only those limitations indicated in the appended claims should be imposed upon the scope of this invention.

What is claimed is:

l. A process for the puriiication of beryllia from the impurities normally associated therewith, comprising heating said beryllia in contact with steam to a temperature from 1000 C. to the melting point of beryllia and cooling the resultant beryllia-containing vapor to yield a condensate of beryllia.

2. A process for the preparation of a beryllia insulating material comprising heating solid beryllia to a temperature between 1200 and 1700 C. in the presence of steam up to about 1 atmosberyllia-containing vapor to yield a condensate of pure beryllia and removing the steam from said condensate.

3. A process for the purication of beryllia from the impurities normally associated therewith comprising heating said beryllia in contact With steam at a temperature of about 1500" C., cooling the beryllia-containing vapors thus formed to condense beryllia, removing the steam, and collecting the cooled beryllia condensate.

4. A process for the purification of beryllia comprising heating beryllia having an aluminumcontaining impurity in contact with steam at a temperature of about 1500 C., cooling the berylia-containing vapor formed thereby to condense beryllia, removing the steam, and collecting the cooled puried beryllia condensate.

JOHN G. MALM. CLYDE A. HUTCI-USON, JR.

No references cited. 

1. A PROCESS FOR THE PURIFICATION OF BERYLLIA FROM THE IMPURITIES NORMALLY ASSOCIATED THEREWITH, COMPRISING HEATING SAID BERYLLIA IN CONTACT WITH STEAM TO A TEMPERATURE FROM 1000*C. TO THE MELTING POINT OF BERYLLIA AND COOLING THE RE- 